The field of the invention relates to internal combustion engines having vacuum assisted brake systems.
There are many engine operating conditions that are either measured or estimated to improve internal combustion engine control. For example, manifold pressure is a common internal combustion engine parameter used in various engine control systems. To determine degradation in a manifold pressure sensor, it is known to estimate manifold pressure from engine mass air flow and engine speed along with known engine relationships. It is also common to improve accuracy of this estimated manifold pressure with manifold temperature and exhaust gas recirculation amounts. Then, degradation in the sensor is determined when the estimated value and measured value disagree.
Conversely, it is also known to estimate mass air flow from manifold pressure. The estimated mass air flow can then be used to determine degradation in the mass air flow sensor. Typically, measured manifold pressure, and also manifold temperature, are used with various predetermined engine maps and engine speed to estimate mass air flow. It is further known to improve accuracy of engine mass air flow by including exhaust gas recirculation amounts.
In addition, it is also known to use throttle position and engine speed as indications of either mass air flow and/or manifold pressure.
The inventors herein have recognized a disadvantage with the above approaches. In particular, such estimation methods can have errors due to engine variation, engine aging, and various other effects. These potential errors can degrade engine performance, fuel economy, and emissions. For example, engine characteristics relating manifold pressure and mass air flow may change from one engine to another. Similarly, engine aging affects may change heat transfer characteristics, thereby causing errors to arise. Then, premature degradation can be indicated when comparing these estimated values to measured values.
An object of the present invention is to improve determination of degradation of various operating conditions.
The above object is achieved and disadvantages of prior approaches overcome by a method for determining operability of a sensor, the sensor for sensing an operating parameter of a vehicle system having an internal combustion engine, the engine having a manifold, the manifold coupled through a check valve to a brake booster, the method comprising: measuring a brake booster pressure; calculating an estimate of the operating parameter based on said brake booster pressure; and determining degradation of the sensor based on said estimate of the operating parameter.
By using brake booster pressure, it is possible to provide an improved estimate of other operating parameters. In other words, the present invention recognizes the relationships between brake booster pressure and other operating parameters and then uses them to improve estimation. Then, from the improved estimates, more accurate determination of degradation can be realized.
An advantage of the above aspect of the present invention is improved degradation determination of operating parameters.
Another advantage of the above aspect of the present invention is that from improved degradation determination, improved fuel economy and emission can be provided.